Method of manufacturing vibration gyro sensor element, vibration gyro sensor element, and method of adjusting vibration direction

ABSTRACT

A drive electrode to which a voltage for allowing a vibrator to vibrate is applied and first and second detection electrodes extending in the longitudinal direction of the vibrator in parallel to each other are formed as the upper electrode such that the drive electrode is interposed between the first and second detection electrodes and does not contact with the detection electrodes. In the case where there is a difference between the detection signals detected in the first and second detection electrodes when a voltage is applied between the lower electrode and drive electrode to allow the vibrator to vibrate at a vertical resonance frequency, a laser light is irradiated to a desired portion of the vibrator to apply grinding operation based on detection signals detected in the first and second detection electrodes, thereby adjusting the shape of the vibrator.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an angular rate sensor for use in videocamera hand movement detection, motion detection in a virtual realityapparatus, direction detection in a car navigation system, or the like,and more particularly, to a method of manufacturing a small-sizedvibration gyro sensor element having a cantilever vibrator, a vibrationgyro sensor element, and a method of adjusting vibration direction.

This application claims priority of Japanese Patent Application No.2004-064239, filed on Mar. 8, 2004, the entirety of which isincorporated by reference herein.

2. Description of the Related Art

So-called a vibration-type gyro sensor (hereinafter, referred to asvibration gyro sensor) has now been widely used as an angular ratesensor for consumer use. The vibration gyro sensor allows a cantilevervibrator to vibrate at a predetermined resonance frequency and detectsCoriolis force caused due to influence of an angular rate using apiezoelectric element, thereby detecting the angular rate.

The vibration gyro sensor is advantageous in its simple mechanism, shortstart-up time, and reduced manufacturing cost, and has now beenincorporated in an electronic apparatus such as a video camera, virtualreality apparatus, or car navigation system, to serve as a sensor forhand movement detection, motion detection, direction detection,respectively.

As the electronic apparatuses in which the vibration gyro sensor isincorporated have become increasingly compact and higher performance,the vibration gyro sensor itself is required to be rendered compact andhigher performance. For example, miniaturization is required to realizemulti-functional electronic apparatus by combining the vibration gyrosensor with various sensors for use in other purposes and mounting themon a substrate.

However, since a vibrator of the vibration gyro sensor is manufacturedby shaping a piezoelectric material obtained by a cutting process withmachine work, processing accuracy in the manufacturing process cannotmeet the requirement for the above miniaturization, so that desiredperformance cannot be obtained.

In order to cope with the problem, a piezoelectric vibration angularrate meter, that is, a vibration gyro sensor in which the vibrator ismanufactured by forming a thin film made of a piezoelectric material ona single-crystal silicon substrate has been devised (referred, forexample, to Jpn. Pat. Appln. Laid-Open Publication Nos. 8-261763 and8-327364).

The vibrator of the vibration gyro sensor needs to be a regular squarepole having a square cross-section in order to detect an angular ratewith stable detection accuracy. However, it is physically very difficultto obtain the vibrator as a perfectly regular square pole in the casewhere the vibrator is manufactured by machine work or in the case wherethe vibrator is manufactured by processing a single-crystal siliconsubstrate with a thin-film formation process, so that the manufacturedvibrator may have an asymmetrical cross-section.

When a drive signal is applied to such an asymmetrical shaped vibratorto cause self-excited vibration, the vibration direction does not followthe center line of the vibrator, but is inclined relative to the centerline of the vibrator. When the vibration direction is inclined asdescribed above, the value of the detection signal to be detected forthe angular rate detection becomes inaccurate, leading to an inaccurateangular rate.

SUMMARY OF THE INVENTION

The present invention has been made to solve the above problem, and anobject thereof is to provide a method of manufacturing a vibration gyrosensor element capable of adequately adjusting the vibration directionof a vibrator of the small-sized vibration gyro sensor elementmanufactured by using a thin film formation process in a state where thevibrator is allowed to vibrate self-excitedly without application of anangular rate, a vibration gyro sensor element, and a method of adjustingvibration direction.

To achieve the above object, according to a first aspect of the presentinvention, there is provided a method of manufacturing a vibration gyrosensor element that includes a cantilever vibrator having a lowerelectrode, a piezoelectric thin film, and an upper electrode, anddetects an angular rate using piezoelectric effect of the piezoelectricthin film. The method comprises the steps of: forming a first protectivefilm pattern including a first opening portion constituted by the linesparallel to and perpendicular to a {110} surface on a first main surfaceof a single-crystal silicon substrate, the first main surface and asecond main surface of the single-crystal silicon substrate opposite tothe first main surface having orientations {100}, and applying crystalanisotropic etching to the first opening portion until the thickness ofthe etched portion becomes the thickness of the vibrator; sequentiallyforming the lower electrode, piezoelectric thin film, and upperelectrode in a stacked manner on the area to become the vibrator, thearea being included in the second main surface opposite to the firstmain surface that has been subjected to the crystal anisotropic etchinguntil the thickness of the etched portion becomes the thickness of thevibrator; forming a second protective film pattern including a secondopening portion having a space that makes the vibrator to be acantilever shape on the second main surface where the lower electrode,piezoelectric thin film, upper electrode have been formed, the secondopening portion being constituted by the lines parallel to andperpendicular to the {110} surface, and forming the vibrator by applyingreactive ion etching (RIE) to the second opening portion; forming, asthe upper electrode, a drive electrode to which a voltage for allowingthe vibrator to vibrate is applied and first and second detectionelectrodes extending in the longitudinal direction of the vibrator inparallel to each other such that the drive electrode is interposedbetween the first and second detection electrodes and does not contactwith the detection electrodes; and irradiating a laser light to adesired portion of the vibrator to apply grinding operation based ondetection signals detected in the first and second detection electrodesin the case where there is a difference between the detection signalsdetected in the first and second detection electrodes, the detectionsignals being obtained when a voltage is applied between the lowerelectrode and drive electrode to allow the vibrator to vibrate at avertical resonance frequency.

To achieve the above object, according to a second aspect of the presentinvention, there is provided a vibration gyro sensor element thatincludes a cantilever vibrator having a lower electrode, a piezoelectricthin film, and an upper electrode, and detects an angular rate usingpiezoelectric effect of the piezoelectric thin film. The elementcomprises the vibrator according to a manufacturing method including thesteps of: forming a first protective film pattern including a firstopening portion constituted by the lines parallel to and perpendicularto a {110} surface on a first main surface of a single-crystal siliconsubstrate, the first main surface and a second main surface of thesingle-crystal silicon substrate opposite to the first main surfacehaving orientations {100}, and applying crystal anisotropic etching tothe first opening portion until the thickness of the etched portionbecomes the thickness of the vibrator; sequentially forming the lowerelectrode, piezoelectric thin film, and upper electrode in a stackedmanner on the area to become the vibrator, the area being included inthe second main surface opposite to the first main surface that has beensubjected to the crystal anisotropic etching until the thickness of theetched portion becomes the thickness of the vibrator; and forming asecond protective film pattern including a second opening portion havinga space that makes the vibrator to be a cantilever shape on the secondmain surface where the lower electrode, piezoelectric thin film, upperelectrode have been formed, the second opening portion being constitutedby the lines parallel to and perpendicular to the {110} surface, andforming the vibrator by applying reactive ion etching (RIE) to thesecond opening portion. The vibrator includes, as the upper electrode, adrive electrode to which a voltage for allowing the vibrator to vibrateis applied and first and second detection electrodes extending in thelongitudinal direction of the vibrator in parallel to each other suchthat the drive electrode is interposed between the first and seconddetection electrodes and does not contact with the detection electrodes,and the vibrator is grinded by irradiating a laser light to a desiredportion of the vibrator based on detection signals detected in the firstand second detection electrodes in the case where there is a differencebetween the detection signals detected in the first and second detectionelectrodes, the detection signals being obtained when a voltage isapplied between the lower electrode and drive electrode to allow thevibrator to vibrate at a vertical resonance frequency.

To achieve the above object, according to a third aspect of the presentinvention, there is provided a method of adjusting vibration directionof the vibrator, the vibrator being a cantilever vibrator having a lowerelectrode, a piezoelectric thin film, and an upper electrode formed on asingle-crystal silicon substrate by a thin film formation process andincluded in a vibration gyro sensor element that detects an angular rateusing piezoelectric effect of the piezoelectric thin film. The methodcomprises the steps of: forming, as the upper electrode, a driveelectrode to which a voltage for allowing the vibrator to vibrate isapplied and first and second detection electrodes extending in thelongitudinal direction of the vibrator in parallel to each other suchthat the drive electrode is interposed between the first and seconddetection electrodes and does not contact with the detection electrodes;and irradiating a laser light to a desired portion of the vibrator toapply grinding operation based on detection signals detected in thefirst and second detection electrodes in the case where there is adifference between the detection signals detected in the first andsecond detection electrodes, the detection signals being obtained when avoltage is applied between the lower electrode and drive electrode toallow the vibrator to vibrate at a vertical resonance frequency.

In the present invention, a drive electrode to which a voltage forallowing the vibrator to vibrate is applied and first and seconddetection electrodes extending in the longitudinal direction of thevibrator in parallel to each other are formed as the upper electrodesuch that the drive electrode is interposed between the first and seconddetection electrodes and does not contact with the detection electrodes.In the case where there is a difference between the detection signalsdetected in the first and second detection electrodes when a voltage isapplied between the lower electrode and drive electrode to allow thevibrator to vibrate at a vertical resonance frequency, a laser light isirradiated to a desired portion of the vibrator to apply grindingoperation based on detection signals detected in the first and seconddetection electrodes, thereby adjusting the shape of the vibrator.

Thus, it is possible to adequately adjust the shape of the vibratorgrinded by the laser light irradiation without using an uncertain methodthat visually observes symmetric property of the vibrator and adjuststhe inclination of the vibration direction caused due to malformation ofthe vibrator before grinding operation. Therefore, the vibration gyrosensor element including the above vibrator can detect an angular ratewith satisfactory detection characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view for explaining a vibration gyro sensorelement shown as a preferred embodiment of the present invention;

FIG. 2 is a view for explaining a configuration of an angular ratesensor including the vibration gyro sensor element;

FIG. 3 is a perspective view for explaining a vibrator included in thevibration gyro sensor element;

FIG. 4 is a plan view for explaining the vibration gyro sensor element;

FIG. 5 is a plan view for explaining a single-crystal silicon substrateused when the vibration gyro sensor element is manufactured;

FIG. 6 is a cross-sectional view when the single-crystal siliconsubstrate shown in FIG. 5 is cut along the line XX;

FIG. 7 is a plan view showing a state where a resist film pattern hasbeen formed on the single-crystal silicon substrate;

FIG. 8 is a cross-sectional view when the single-crystal siliconsubstrate shown in FIG. 7 is cut along the line XX;

FIG. 9 is a plan view showing a state where a thermally-oxidized filmhas been removed from the single-crystal silicon substrate;

FIG. 10 is a cross-sectional view when the single-crystal siliconsubstrate shown in FIG. 9 is cut along the line XX;

FIG. 11 is a plan view showing a state where the single-crystal siliconsubstrate has been subjected to crystal anisotropic etching;

FIG. 12 is a cross-sectional view when the single-crystal siliconsubstrate shown in FIG. 11 is cut along the line XX;

FIG. 13 is a cross-sectional view showing the area A of FIG. 12 in anenlarged manner;

FIG. 14 is a plan view showing a state of the front surface side of thesingle-crystal silicon substrate;

FIG. 15 is a cross-sectional view when the single-crystal siliconsubstrate shown in FIG. 14 is cut along the line XX;

FIG. 16 is a plan view showing a state of the single-crystal siliconsubstrate on which a lower electrode film, a piezoelectric film, and anupper electrode film have been formed;

FIG. 17 is a cross-sectional view when the single-crystal siliconsubstrate shown in FIG. 16 is cut along the line XX;

FIG. 18 is a plan view showing a state of the single-crystal siliconsubstrate on which a drive electrode and detection electrodes have beenformed;

FIG. 19 is a cross-sectional view when the single-crystal siliconsubstrate shown in FIG. 18 is cut along the line XX;

FIG. 20 is a plan view showing a state of the single-crystal siliconsubstrate on which a piezoelectric body has been formed;

FIG. 21 is a cross-sectional view when the single-crystal siliconsubstrate shown in FIG. 20 is cut along the line XX;

FIG. 22 is a plan view showing a state of the single-crystal siliconsubstrate on which a reference electrode has been formed;

FIG. 23 is a cross-sectional view when the single-crystal siliconsubstrate shown in FIG. 22 is cut along the line XX;

FIG. 24 is a plan view showing a state of the single-crystal siliconsubstrate on which a planarizing resist film has been formed;

FIG. 25 is a cross-sectional view when the single-crystal siliconsubstrate shown in FIG. 24 is cut along the line YY;

FIG. 26 is a plan view showing a state of the single-crystal siliconsubstrate on which wire connection terminals have been formed;

FIG. 27 is a cross-sectional view when the single-crystal siliconsubstrate shown in FIG. 26 is cut along the line YY;

FIG. 28 is a plan view showing a state of the single-crystal siliconsubstrate in which a surrounding space has been formed around thevibrator by reactive ion etching;

FIG. 29 is a cross-sectional view when the single-crystal siliconsubstrate shown in FIG. 28 is cut along the line YY;

FIG. 30 is a cross-sectional view when the single-crystal siliconsubstrate shown in FIG. 28 is cut along the line XX;

FIG. 31 is a plan view showing a state of the single-crystal siliconsubstrate on which a plurality of vibration gyro sensor elements havebeen formed;

FIG. 32 is a plan view showing cutting plane lines to indicate where theplurality of vibration gyro sensor elements formed on the single-crystalsilicon substrate are cut;

FIG. 33 is a plan view showing a state where the vibration gyro sensorelements are attached to an IC substrate;

FIG. 34 is a plan view showing a state where a cover member is attachedto the angular rate sensor including the vibration gyro sensor element;

FIG. 35 is a plan view showing the vibration gyro sensor element thatadjusts the shape of the vibrator by means of laser irradiation;

FIG. 36 is a vertical cross-sectional view of the vibrator having anideal cross-section;

FIG. 37 is a vertical-cross sectional view of the vibrator having anasymmetrical shape with respect to the central axis;

FIG. 38 is a view showing a state of the vibration caused by allowingthe vibrator shown in FIG. 36 to vibrate self-excitedly;

FIG. 39 is a view showing a state of the vibration caused by allowingthe vibrator shown in FIG. 37 to vibrate self-excitedly;

FIG. 40 is a flowchart for explaining a process to adjust the vibrationdirection of the vibrator by a grinding operation with respect to thevibrator with laser irradiation;

FIG. 41 is a view for explaining a processing area on the back sidesurface of the vibrator to be irradiated by the leaser beam;

FIG. 42 is a view for explaining a processing area on the front sidesurface of the vibrator to be irradiated by the leaser beam;

FIG. 43 is a view for explaining the irradiation point of the laser beamon the processing area of the vibrator;

FIG. 44 is a graph showing a change in the number of processing cyclesdepending on the difference in the irradiation point of the laser beam;and

FIG. 45 is a graph showing a change in the number of processing cyclesdepending on the difference in the irradiation point of the laser beam.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferred embodiment of a manufacturing method of a vibration gyrosensor element, a vibration gyro sensor elements, and a method ofadjusting vibration direction according to the present invention will bedescribed below in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view showing a vibration gyro sensor element 10included in an angular rate sensor 50 to which the present invention isapplied, and FIG. 2 is a view showing an example of a circuitconfiguration of the angular rate sensor 50. A part of the vibrationgyro sensor element 10 of FIG. 1 is shown in a transparent manner forillustrative purposes.

As shown in FIG. 1, the vibration gyro sensor element 10 has so-called acantilever vibrator 11. The vibrator 11 is formed as a beam having fixedone end by providing a surrounding space 12 around the vibrator 11 in anelement having a thickness of t1, length of t2, and width of t3 obtainedby cutting a silicon single-crystal substrate. Around the vibrator 11,space widths of t7 b and t7 c in the direction perpendicular to thelongitudinal direction of the vibrator 11, and a space width of t7 a inthe longitudinal direction thereof are ensured. Note that t7 b and t7 care the same length.

The vibrator 11 is formed as a square pole having a square cross-sectionobtained when the vibrator 11 is cut along a plane perpendicular to thelongitudinal direction thereof.

The vibration gyro sensor element 10 can have, for example, the size oft1=300 μm, t2=3 mm, and t3=1 mm, assuming that the thickness, length,width of the element are t1, t2, and t3, respectively, as describedabove. The size of the vibrator 11 at this time can be set to, forexample, t4=100 μm, t5=2.5 mm, and t6=100 μm, assuming that thethickness, length, width of the vibrator are t4, t5, and t6,respectively, as shown in FIG. 3.

FIG. 4 is a plan view of the vibration gyro sensor element 10. As shownin FIG. 4, a reference electrode 4 a and a piezoelectric body 5 a aresequentially stacked on the vibrator 11. Further, on the piezoelectricbody 5 a, a pair of detection electrodes 6 b and 6 c and a driveelectrode 6 a interposed between the pair of detection electrodes 6 band 6 c are formed in such a manner that they extend in parallel to eachother in the longitudinal direction of the vibrator 11 and that they arenot in contact with each other. Wire connection terminals A, B, C, and Dare provided for the drive electrode 6 a, detection electrodes 6 b and 6c, and reference electrode 4 a, respectively.

The piezoelectric body 5 a is a thin film made of, for example,piezoelectric ceramics such as lead zirconate titanate (PZT), orpiezoelectric single crystal such as quartz or LaTaO₃.

The vibration gyro sensor element 10 having the above configurationoperates by connecting to an IC circuit 40 shown in FIG. 2 and functionsas the angular rate sensor 50 to detect Coriolis force generated inaccordance with the angular rate.

The IC circuit 40 includes an adder circuit 41, an amplifier circuit 42,a phase shift circuit 43, an AGC (Automatic Gain Control) 44, adifferential amplifier circuit 45, a synchronous detection circuit 46,and a smoothing circuit 47.

The pair of detection electrodes 6 b and 6 c of the vibration gyrosensor element 10 are connected to the adder circuit 41 and differentialamplifier circuit 45, respectively via the wire connection terminals Band C. The drive electrode 6 a of the vibration gyro sensor element 10is connected to the output terminal of the AGC 44 via the wireconnection terminal A.

In the angular rate sensor 50, the adder circuit 41, amplifier circuit42, phase shift circuit 43, AGC 44 and vibration gyro sensor element 10constitute so-called a phase shift oscillator, which applies voltagebetween the reference electrode 4 a and drive electrode 6 a to allow thevibrator to vibrate self-excitedly. The vibration direction of thevibrator 11 corresponds to the thickness direction of the vibrator 11.

Further, in the angular rate sensor 50, the output terminals of theadder circuit 41 and differential amplifier circuit 45 whose inputterminals are connected to the pair of detection electrodes 6 b and 6 cvia the wire connection terminals B and C are connected to thesynchronous detection circuit 46, which is then connected to thesmoothing circuit 47. The combination of the above components and thepiezoelectric body 5 a functions as a detection section that detects theangular rate of the vibrator 11.

More specifically, in the angular rate sensor 50 shown in FIG. 2, whenan angular rate is applied to the vibrator 11 in the longitudinaldirection thereof while the vibrator 11 of the vibration gyro sensorelement 10 is allowed to vibrate self-excitedly by the above phase shiftoscillator, Coriolis force is generated in a direction perpendicular tothe vibration direction of the vibrator 11. The generated Coriolis forceis detected by the piezoelectric body 5 a, and the detection resultoutput from the detection electrodes 6 b and 6 c as signals withreversed polarity to each other is input to the differential amplifiercircuit 45. The output amplified by the differential amplifier circuit45 is input to the synchronous detection circuit 46, where thesynchronous detection is performed. In order for the synchronousdetection to be performed, the output from the adder circuit 41 issupplied as a synchronous signal to the synchronous detection circuit46. The output from the synchronous detection circuit 46 is finallyoutput via the smoothing circuit 47 as an angular rate signal, which isa direct current signal obtained by detecting the Coriolis forcegenerated in the vibrator 11.

As described above, the angular rate sensor 50 uses the piezoelectricbody 5 a to allow the vibrator 11 to vibrate and to detect the Coriolisforce generated in the vibrator 11, and the angular rate can be detectedbased on the Coriolis force detected by the piezoelectric body 5 a.

EXAMPLE

A manufacturing method of the above vibration gyro sensor element 10will next be described as an example.

As described above, the vibration gyro sensor element 10 shown in FIG. 1is formed by processing a single-crystal silicon substrate.

FIG. 5 is a plan view of the single-crystal silicon substrate 1 usedwhen the vibration gyro sensor element 10 is manufactured. FIG. 6 is across-sectional view when the single-crystal silicon substrate 1 shownin FIG. 5 is cut along the line XX. One main surface 1B and the othermain surface 1A of the single-crystal silicon substrate 1 are subjectedto thermal oxidation so as to form SiO₂ films respectively on both themain surfaces. The SiO₂ film serves as a protective film in step ofcrystal anisotropic etching to be described later.

The single-crystal silicon substrate 1 used for the vibration gyrosensor element 10 is cut out such that the one main surface 1B of thesingle-crystal silicon substrate 1 has a surface orientation {100} asshown in FIG. 5, and the side surface 1C has a surface orientation {110}as shown in FIG. 6. Since the other main surface 1A is in parallel tothe one main surface 1B, the surface orientation of the other mainsurface 1A is also {100}.

It is assumed that “{ }” is a symbol for collectively representingequivalent surface orientations among which the directions are differentfrom each other, and, for example, {100} collectively represents (100),(010), (001), and the like.

The size of the single-crystal silicon substrate 1 to be cut out withthe crystal surface orientations defined as described above isarbitrarily set depending on a machine provided on a manufacturing line.For example, the single-crystal silicon substrate 1 has a size of 3centimeters by 3 centimeters in the present example.

While the thickness of the single-crystal silicon substrate 1 isdetermined in consideration of workability or the price of thesubstrate, it is sufficient for the single-crystal silicon substrate 1to have at least a thickness greater than the thickness of the vibrator11 formed in the vibration gyro sensor element 10. For example, in thepresent example, since the thickness t4 of the vibrator 11 is set to 100μm as shown in FIG. 3, the thickness of the single-crystal siliconsubstrate 1 is set to 300 μm that is three times greater than thethickness of the vibrator 11.

As shown in FIG. 6, the one main surface 1B and the other main surface1A of the single-crystal silicon substrate 1 are subjected to thermaloxidation so as to form thermally-oxidized films 2A and 2B, which areSiO₂ films, respectively on both the main surfaces. Thethermally-oxidized films 2A and 2B serve as a protective film in step ofcrystal anisotropic etching to be described later. The thicknesses ofthe thermally-oxidized films 2A and 2B can be arbitrarily determined,and are set to 0.1 μm in the present example. Further, while asingle-crystal silicon substrate 1 of N-conductive type is employed inthe present example, the conductive type can be arbitrarily determined.

Hereinafter, in the single-crystal silicon substrate 1, the other mainsurface 1A on which the thermally-oxidized film 2A has been formed isassumed to be “front surface”, and the one main surface 11B on which thethermally-oxidized film 2B has been formed is assumed to be “backsurface”.

The above single-crystal silicon substrate 1 is used to manufacture thevibration gyro sensor element 10, in practice. Firstly, on the backsurface of the single-crystal silicon substrate 1, thethermally-oxidized film 2B that has been formed in the portion to besubjected to crystal anisotropic etching is removed by photoetching.

The photoetching to be performed is roughly divided into two steps: astep of forming a resist film pattern having openings corresponding tothe portions to be removed on the thermally-oxidized film 2B(photolithography) and a step of removing the thermally-oxidized film 2Busing the pattern (etching).

FIG. 7 is a plan view showing a state where a resist film pattern 3 hasbeen formed on the thermally-oxidized film 2B of the single-crystalsilicon substrate 1, and FIG. 8 is a cross-sectional view when thesingle-crystal silicon substrate 1 shown in FIG. 7 is cut along the lineXX.

As shown in FIG. 7, the resist film pattern 3 formed on thethermally-oxidized film 2B has opening portions 3 a arranged regularlyat predetermined intervals. Each of the opening portions 3 a has arectangular shape having a size of t8 by t9, t8 being the length in adirection perpendicular to the {110} surface, and t9 being the length inparallel to the {110} surface. In the present example, 3 by 5 openingportions 3 a are formed in the pattern. Each of the opening portions 3 afunctions as a vibration gyro sensor element 10.

The resist film pattern 3 is formed in a manner entirely similar tophotolithography used in semiconductor manufacturing process. That is,after microwave has been used to perform prebaking to heat thethermally-oxidized film 2B in order to remove moisture, a photo resistfilm made of photosensitive resin is coated onto the surface of thethermally-oxidized film 2B. Thereafter, a mask having the above patternfor forming the opening portions 3 a is exposed onto the photo resistfilm, followed by development.

The lengths of the t8 and t9 that define each of the opening portions 3a are determined by the shape of the vibrator 11 formed in the vibrationgyro sensor element 10, thickness t1 of the single-crystal siliconsubstrate 1, and space widths t7 a, t7 b, and t7 c around the vibratorshown in FIG. 1. Concrete numerical values of t8 and t9 will bedescribed later in detail.

In this manner, the resist film pattern 3 has been formed on thethermally-oxidized film 2B of the single-crystal silicon substrate 1 asshown in FIG. 8.

Subsequently, the thermally-oxidized film 2B corresponding to theopening portions 3 a formed by the resist film pattern 3 is removed byetching. FIG. 9 is a plan view showing a state where thethermally-oxidized film 2B corresponding to the opening portions 3 aformed by the resist film pattern 3 has been removed. FIG. 10 is across-sectional view when the single-crystal silicon substrate 1 shownin FIG. 9 is cut along the line XX.

While the etching method used to remove the thermally-oxidized film 2Bmay be physical etching, such as ion etching, or wet etching, it ispreferable to use wet etching that allows only the thermally-oxidizedfilm 2B to be removed when the smoothness of the interface of thesingle-crystal silicon substrate 1 is taken into consideration.

In the present example, ammonium fluoride is used as chemicals in thewet etching. However, when the wet-etching is performed for a long time,etching proceeds from the side surface of the opening portion, that is,so-called side etching proceeds. Therefore, it is necessary to exactlycontrol the etching time so that the etching is terminated at the timepoint when only the thermally-oxidized film 2B corresponding to theopening portions 3 a has been removed.

In this manner, the thermally oxidized film 2B corresponding to theopening portions 3 a of the resist film pattern 3 has been removed asshown in FIG. 10.

When the thermally oxidized film 2B has been removed by theabove-mentioned etching, opening portions 2Ba each having a size of t8by t9, which is the same as the size of each of the opening portions 3 aof the resist film pattern 3, exposes the {100} surface of thesingle-crystal silicon substrate 1. The single-crystal silicon substrate1 in this state is then subjected to the wet etching to reduce thethickness thereof to t4, which corresponds to the thickness of thevibrator 11.

FIG. 11 is a plan view showing a state where the thermally-oxidized film2B corresponding to the opening portions 3 a has been removed and onlythe opening portions 2Ba, each having a size of t8 by t9, through whichthe {100} surface of the single-crystal silicon substrate 1 is exposedhas been etched, FIG. 12 is a cross-sectional view when thesingle-crystal silicon substrate 1 shown in FIG. 11 is cut along theline XX, and FIG. 13 is a cross-sectional view showing the area A ofFIG. 12 in an enlarged manner.

The wet etching applied to the single-crystal silicon substrate 1 iscrystal anisotropic etching taking advantage of the nature that etchingrate depends upon crystal orientation. When the crystal anisotropicetching is applied to the opening portions 2Ba obtained by removing thethermally-oxidized film 2B and through which the {100} surface isexposed, {111} surface that is a surface orientation with an angle ofabout 55° relative to the {100} surface appears as shown in FIG. 13.When the etching has been applied with the thickness corresponding tot4, which is the thickness of the vibrator 11, assured, so called adiaphragm shape has been obtained.

In general, the single-crystal silicon has a crystal structureexhibiting etching rate dependency on the crystal orientation. That is,the {111} surface is more hardly etched than the {100} surface. To bespecific, the etching rate of the {100} surface of the single-crystalsilicon is 200 times higher than that of the {111} surface.

Etching solutions that can be used when the crystal anisotropic etchingis applied to the single-crystal silicon include TMAH (tetramethylammonium hydroxide), KOH (potassium hydroxide), EDP(ethylenediamine-pyrocathecol-water), and hydrazine.

In the present example, TMAH (tetramethyl ammonium hydroxide) 20 wt %solution that allows the etching rate selectivity between thethermally-oxidized films (2A and 2B) and the single-crystal silicon tobe further increased was used. At the time of etching, the etchingsolution was stirred to maintain the temperature of the solution at 80°C. In this state, the etching was performed for six hours until thedepth t10 of the diaphragm had become 200 μm, that is, the thickness t11of the single-crystal silicon substrate 1 to be remained after etchinghad become 100 μm, which corresponds to the thickness t4 of the vibrator11.

A concrete description will be given of the numerical values of t8 andt9 that define the size of the opening portion 3 a, which has beenformed by means of the resist film pattern 3 of FIG. 7 for thesubsequent crystal anisotropic etching.

The width t9 of the opening portion 3 a, that is, the width of thediaphragm after etching is represented by the equation: t9=t9 a+t9 b+t9c, as shown in FIG. 13.

t9 c can be represented by the following equation, using the width t6 ofthe vibrator 11 shown in FIG. 3 and space widths t7 b and t7 c of thesurrounding space 12 of FIG. 1 formed around the vibrator 11: t9 c=t6+t7b+t7 c.

Further, the {111} surface that appears after the crystal anisotropicetching and {100} surface which is the back surface of thesingle-crystal silicon substrate 1 form an angle of 55° as shown in FIG.13. Therefore, t9 a and t9 b, which are the same value, can berepresented by the following equation, using the depth t10 of thediaphragm: t9 a=t9 b=t10×1/tan 55°.

Accordingly, the width t9 of the opening portion 3 a can be representedby the equation: t9={t10×1/tan 55°}×2+(t6+t7 b+t7 c). Assuming thatt6=100 μm, t7 b=t7 c=200 μm, and t10=200 μm, 780 μm is obtained as t9.

After the above crystal anisotropic etching has been performed, {111}surface that is a surface orientation with an angle of about 55°relative to the {100} surface appears also in t8 direction as well as int9 direction. Accordingly, the length t8 of the opening portion, thatis, the length of the diaphragm after etching is represented by thefollowing equation, using the length t5 of the vibrator 11 of FIG. 3 andspace width t7 a of the surrounding space 12 of FIG. 1 formed around thevibrator 11: t8={t10×1/tan 55°×}×2+(t5+t7 a). Assuming that t5=2.5 mm,t7 a=200 μm, and t10=200 μm, 29801 m is obtained as t8.

Although the entire configuration of the single-crystal siliconsubstrate 1 has been described in the foregoing, the followingdescription will be given of only one single-crystal silicon substrate 1on which the diaphragm has been formed, which corresponds to an area Wshown in FIG. 11 for simplicity of explanation. Further, since thefollowing description relates to a processing step for thethermally-oxidized film 2A side, plan views in which thethermally-oxidized film 2A, which is the front surface, is set as theupper surface, and cross-sectional views each obtained when the planview is cut along a predetermined position are used.

To be more precise, when the thermally-oxidized film 2A of thesingle-crystal silicon substrate 1 on which the diaphragm of the area Wshown in FIG. 11 has been formed is set as the upper surface, the planview as shown in FIG. 14 and corresponding cross-sectional view as shownin FIG. 15 taken along the line XX are obtained.

Subsequently, a lower electrode film, a piezoelectric film, and an upperelectrode film are deposited on the thermally-oxidized film 2A forformation of the reference electrode 4 a, piezoelectric body 5 a, driveelectrode 6 a, and detection electrodes 6 b and 6 c. FIG. 16 is a planview showing a state where the lower electrode film 4, piezoelectricfilm 5, and upper electrode film 6 are deposited on thethermally-oxidized film 2A of the single-crystal silicon substrate 1,and FIG. 17 is a cross-sectional view taken along the line XX in FIG.16.

In the present example, the lower electrode film 4, piezoelectric film5, and upper electrode film 6 are deposited using a magnetron sputteringmachine.

Firstly, the lower electrode film 4 is deposited on thethermally-oxidized film 2A. In the present example, titanium (Ti) wasdeposited to a film thickness of 50 nm on the thermally-oxidized film 2Aunder a magnetron sputtering condition of gas pressure: 0.5 Pa, RFpower: 1 kw. Subsequently, platinum was deposited to a film thickness of200 nm on the deposited titanium (Ti) under a magnetron sputteringcondition of gas pressure: 0.5 Pa, RF power: 0.5 kw. That is, thedeposited titanium and platinum having the above thicknesses constitutethe lower electrode film 4.

After that, the piezoelectric film 5 is deposited on the lower electrodefilm 4. In the present example, withPb_((1+x))(Zr_(0.53)Ti_(0.47))O_(3−y) oxide used as a target, leadzirconate titanate (PZT) piezoelectric thin film was deposited to a filmthickness of 1 μm on the platinum (Pt) deposited as the lower electrodefilm 4 under a magnetron sputtering condition of room temperature, gaspressure: 0.7 Pa, RF power: 0.5 kw. Subsequently, the single-crystalsilicon substrate 1 on which lead zirconate titanate (PZT) film had beenformed was put into an electric furnace and crystallization heattreatment was conducted under an oxygen atmosphere at 700° C. for 10minutes to form the piezoelectric film 5.

Finally, the upper electrode film 6 is deposited on the piezoelectricfilm 5. In the present example, platinum (Pt) was deposited to a filmthickness of 200 nm on the piezoelectric film 5 under a magnetronsputtering condition of gas pressure: 0.5 Pa, RF power: 0.5 kw.

Next, the obtained upper electrode film 6 is processed to form the driveelectrode 6 a and detection electrodes 6 b and 6 c. FIG. 18 is a planview showing a state of the single-crystal silicon substrate 1 on whicha drive electrode 6 a and detection electrodes 6 b and 6 c have beenformed, and FIG. 19 is a cross-sectional view when the single-crystalsilicon substrate 1 shown in FIG. 18 is cut along the line XX.

The drive electrode 6 a serves to apply voltage for driving the vibrator11 as described above, and is formed to position at the center of thevibrator 11. The detection electrodes 6 b and 6 c serve to detect theCoriolis force generated in the vibrator 11 as described above and areformed on the vibrator 11 in such a manner to extend in parallel to thedrive electrode 6 a and not to contact with the drive electrode 6 a.

As shown in FIG. 18, each of the drive electrode 6 a and detectionelectrodes 6 b and 6 c has one edge portion aligned with a root line Rwhich is a root of the vibrator 11, and terminal joint portions 6 a ₁, 6b ₁, and 6 c ₁ are formed at the one edge portions of the aboveelectrodes, respectively.

In the present example, the width t13 of the drive electrode 6 a is setto 50 μm, the width t14 of the detection electrodes 6 b and 6 c is setto 10 μm, the length t12 of the drive electrode 6 a and detectionelectrodes 6 b and 6 c is set to 2 mm, and the interval t15 between thedrive electrode 6 a and each of the detection electrodes 6 b and 6 c isset to 5 μm. The sizes of the drive electrode 6 a and detectionelectrodes 6 b and 6 c can be arbitrarily set as far as they are formedwithin the size of the vibrator 11. Further, in the present example, thelength t16 and the width t17 of the terminal joint portions 6 a ₁, 6 b₁, and 6 c ₁, are set to 50 μm, and 50 μm, respectively.

In the present embodiment, after the resist film pattern had been formedon the upper electrode film 6 using a photolithography technique,unnecessary portions of the electrode film 6 were removed by ionetching, thereby forming the drive electrode 6 a, detection electrodes 6b and 6 c, and terminal joint portions 6 a ₁, 6 b ₁, and 6 c ₁.

The present invention is not limited to the above method of forming thedrive electrode 6 a, detection electrodes 6 b and 6 c, and terminaljoint portions 6 a ₁, 6 b ₁, and 6 c ₁, and various method other thanthe above can be used in the present invention.

Next, the piezoelectric film 5 is processed to form the piezoelectricbody 5 a on the vibrator 11. FIG. 20 is a plan view showing a state ofthe single-crystal silicon substrate 1 on which a piezoelectric body 5 ahas been formed by processing the piezoelectric film 5, and FIG. 21 is across-sectional view when the single-crystal silicon substrate 1 shownin FIG. 20 is cut along the line XX.

The piezoelectric body 5 a can be any shape as far as it completelycovers the drive electrode 6 a, and detection electrodes 6 b and 6 c,which are formed from the upper electrode film 6.

In the present example, the length t18 of the piezoelectric body 5 a isset to 2.2 mm, and the width t19 thereof is set to 90 μm. Thepiezoelectric body 5 a having the above size is formed such that thecenter thereof corresponds to the center of the vibrator 11 and one edgeof the piezoelectric body 5 a aligns with the root line R which is aroot of the vibrator 11.

The width t18 of the piezoelectric body 5 a needs to be no greater thanthe width t4 of the vibrator 11. In the present example, thepiezoelectric film 5 is allowed to remain under the aforementionedterminal joint portions 6 a ₁, 6 b ₁, and 6 c ₁, in such a manner to runoff each of the periphery of the terminal joint portions 6 a ₁, 6 b ₁,and 6 c ₁ by 5 μm, respectively. The size of the piezoelectric film 5allowed to remain under the aforementioned terminal joint portions 6 a₁, 6 b ₁, and 6 c ₁ is arbitrarily set depending on the shape and sizeof the entire vibration gyro sensor element 10.

In the present example, after the resist film pattern having a shapecorresponding to the piezoelectric body 5 a and the piezoelectric film 5allowed to remain under the aforementioned terminal joint portions 6 a₁, 6 b ₁, and 6 c ₁ was formed using a photolithography technique,unnecessary portions of the piezoelectric film 5 were removed by wetetching using hydrofluoric-nitric acid solution, thereby forming thepiezoelectric body 5 a.

As described above, the wet etching is used to remove the unnecessaryportions of the piezoelectric film 5 in order to form the piezoelectricbody 5 a in the present example. Alternatively, however, ion etchingwhich is a physical etching technique or reactive ion etching (RIE) thatutilizes chemical and physical effects can be used for the removal inthe present invention.

Next, the lower electrode film 4 is processed to form the referenceelectrode 4 a of the vibrator 11. FIG. 22 is a plan view showing a stateof the single-crystal silicon substrate 1 on which the referenceelectrode 4 a has been formed by processing the lower electrode film 4,and FIG. 23 is a cross-sectional view when the single-crystal siliconsubstrate 1 shown in FIG. 22 is cut along the line XX.

The reference electrode 4 a can be any shape as far as it completelycovers the piezoelectric body 5 a formed by processing the piezoelectricfilm 5.

In the present example, the length t20 of the reference electrode 4 a isset to 2.3 mm, and the width t21 thereof is set to 94 μm. The referenceelectrode 4 a having the above size is formed such that the centerthereof corresponds to the center of the vibrator 11 and one edge of thereference electrode 4 a aligns with the root line R which is a root ofthe vibrator 11.

The width t20 of the reference electrode 4 a needs to be no greater thanthe width t4 of the vibrator 11. In the present example, the lowerelectrode film 4 is allowed to remain under the piezoelectric film 5that is not removed as described above in such a manner to run off theperiphery of the piezoelectric film 5 by 5 μm. The size of the portionthat runs off the periphery of the piezoelectric film 5 is arbitrarilyset depending on the shape and size of the entire vibration gyro sensorelement 10.

Further, for electrical connection between the reference electrode 4 aand the outside, a wire connection terminal D is formed from the lowerelectrode film 4 as shown in FIG. 22. As described above, the referenceelectrode 4 a and wire connection terminal D are electrically connectedto each other through the lower electrode film 4 that is allowed toremain under the piezoelectric film 5.

In the present example, electrical connection between the vibration gyrosensor element 10 and the outside is set to be made by wire bonding, sothat the area for a terminal portion of the wire connection terminal Dto be actually installed should be ensured by the area needed at thewire bonding time.

In the present example, the length t22 of the wire connection terminal Dis set to 200 μm, and the width t23 thereof is set to 100 μm. Theconnection between the vibration gyro sensor element 10 and the outsidecan be any configuration including the connection method. The shape ofthe wire connection terminal D is set depending on the connection methodto be employed to obtain the optimal condition.

In the present example, after forming the resist film pattern having ashape as shown in FIG. 22 using a photolithography technique,unnecessary portions of the lower electrode film 4 were removed by ionetching, thereby forming the reference electrode 4 a, wire connectionterminal D, and lower electrode film 4 that electrically connects thereference electrode 4 a and wire connection terminal D.

As described above, the ion etching, which is a physical etchingtechnique, is used to remove the unnecessary portions of the lowerelectrode film 4 in order to form the reference electrode 4 a in thepresent example. Alternatively, however, wet etching which is a chemicaletching technique or reactive ion etching (RIE) that utilizes chemicaland physical effects can be used for the removal in the presentinvention.

Next, a planarizing resist film 7 is formed so as to smooth electricalconnection between the terminal joint portions 6 a ₁, 6 b ₁, and 6 c ₁formed at the one edges of the drive electrode 6 a and detectionelectrodes 6 b and 6 c, and the wire connection terminals A, B, and C,respectively.

FIG. 24 is a plan view showing a state of the single-crystal siliconsubstrate 1 on which the planarizing resist film 7 has been formed, andFIG. 25 is a cross-sectional view when the single-crystal siliconsubstrate 1 shown in FIG. 24 is cut along the line YY.

As shown in FIG. 22, the physical connection between the wire connectionterminals A, B, and C and terminal joint portions 6 a ₁, 6 b ₁, and 6 c₁ should be made through the end portion of the piezoelectric film 5allowed to remain when the piezoelectric body 5 a is formed and the endportion of the lower electrode film 4 allowed to remain when thereference electrode 4 a is formed.

In the present example, the piezoelectric body 5 a is formed by etchingthe piezoelectric film 5 with a wet etching process. The end portionthat has been subjected to the etching process becomes in a reversetapered shape or vertical form toward the single-crystal siliconsubstrate 1. Therefore, when a wiring film is formed so as toelectrically connect the terminal joint portions 6 a ₁, 6 b ₁, and 6 c ₁and the wire connection terminals A, B, and C, respectively withoutforming the planarizing resist film 7, the electrical connection may bereleased due to step of the end portion.

Further, since the end portion of the lower electrode film 4electrically connected to the reference electrode 4 a is exposed, ashort-circuit may be caused between the drive electrode 6 a, detectionelectrode 6 b and 6 c, and reference electrode 4 a unless theplanarizing resist film 7 is formed.

For the above reason, the planarizing resist film 7 is formed on theterminal joint portions 6 a ₁, 6 b ₁, and 6 c ₁ as shown in FIG. 24 toeliminate step of the end portion of the piezoelectric film 5 and toprevent the end portion of the lower electrode film 4 from beingexposed.

The planarizing resist film 7 can be formed in any shape as far as itcan eliminate step of the end portion of the piezoelectric film 5 andcan prevent the end portion of the lower electrode film 4 from beingexposed. In the present example, the width t24 of the planarizing resistfilm 7 is set to 200 μm, and the length t25 thereof is set to 50 μm.

The planarizing resist film 7 is hardened by applying heat treatment ofabout 280 to 300° C. to the resist film that has been patterned using aphotolithography technique at the portion shown in FIG. 24 in adesirable shape. While the thickness of the resist film is set to about2 μm in the present example, it is preferable that the thickness thereofbe controlled in accordance with the thicknesses of the piezoelectricfilm 5 and lower electrode film 4, and set to no less than the totalthickness of the two. While the planarizing resist film 7 has beenformed using the resist film in the present example, any material can beused with any method as far as it is a non-conducting material that canavoid the above problems.

Next, the wire connection terminals A, B, and C used in performingwiring processing for connecting the drive electrode 6 a and detectionelectrodes 6 b and 6 c with the outside. FIG. 26 is a plan view showinga state of the single-crystal silicon substrate 1 on which wireconnection terminals A, B, and C have been formed. FIG. 27 is across-sectional view when the single-crystal silicon substrate 1 shownin FIG. 26 is cut along the line YY.

The wire connection terminals A, B, and C shown in FIG. 26 are connectedto the terminal joint portions 6 a ₁, 6 b ₁, and 6 c ₁ of the driveelectrode 6 a, and detection electrode 6 b and 6 c, respectively. In thepresent example, electrical connection between the vibration gyro sensorelement 10 and the outside is set to be made by wire bonding, so thatthe areas for terminal portions of the wire connection terminals A, B,and C to be actually installed should be ensured by the area needed atthe wire bonding time, as in the case of the wire connection terminal Ddescribed above.

The wire connection terminals A, B, and C are formed on thethermally-oxidized film 2A in such a manner to be passed through theupper surface of the planarizing resist film 7 and be in contact withthe terminal joint portions 6 a ₁, 6 b ₁, and 6 c ₁. While the shape ofeach of electrode joint portions between the wire connection terminalsA, B, and C, and terminal joint portions 6 a ₁, 6 b ₁, and 6 c ₁ can bearbitrarily formed, it is preferable that the electrode joint portionhave a size greater than 5 μm square.

In the wire connection terminals A, B, and C, the area for terminalportion to be actually installed is formed of the shape that can ensurethe area needed at the wire bonding time, as described above.

In the present example, the length t26 of each of the terminal portionsof the wire connection terminals A, B, and C is set to 200 μm, and thewidth t27 thereof is set to 100 μm. The connection between the vibrationgyro sensor element 10 and the outside can be any configurationincluding the connection method. The shape of the wire connectionterminals A, B, and C is set depending on the connection method to beemployed to obtain the optimal condition.

In the present example, after the resist film pattern having a shape asshown in FIG. 26 had been formed by a photolithography technique, thewire connection terminals A, B, C were formed by sputtering. The filmadhere to unnecessary portions in the sputtering was simultaneouslyremoved at the time of removing the resist film pattern by so-called alift-off method.

More specifically, the wire connection terminals A, B, and C is formedby depositing titanium (Ti) for increasing adherence by 20 nm, low costcopper (Cu) having low electrical resistance is deposited by 300 nm, andgold (Au) is deposited by 300 nm so as to facilitate connection betweenthe wire bonding and each of the wire connection terminals A, B, and C.Any material can be used as the wire connection terminals A, B, and Cand any method can be used to manufacture the wire connection terminalsA, B, and C, and the present invention is not limited to theabove-mentioned materials and method.

Subsequent process is to form the surrounding space 12 for the vibrationgyro sensor 10 as shown in FIG. 1, thereby obtaining the cantilevervibrator 11. FIG. 28 is a plan view showing a state where the cantilevervibrator 11 has been obtained by forming the surrounding space 12 in thesingle-crystal silicon substrate 1, FIG. 29 is a cross-sectional viewwhen the single-crystal silicon substrate 1 shown in FIG. 28 is cutalong the line YY, and FIG. 30 is a cross-sectional view when thesingle-crystal silicon substrate 1 shown in FIG. 28 is cut along theline XX.

As shown in FIG. 28, the surrounding space 12 is a U-shaped spaceconstituted by the space having widths t7 b and t7 c in the left andright directions from the side surfaces of the vibrator 11 on the sidewhere the detection electrodes 6 b and 6 c have been formed, and thespace having a width t7 a in the longitudinal direction at the endportion on the side opposite to the root line R of the vibrator 11.

In the present example, the widths t7 a and t7 b are set to 200 μm,respectively, which are determined based on the state of gas within thesurrounding space 12 and a Q-value representing the required quality ofthe vibration of the vibrator 11.

In the present example, after the resist film pattern having a U-likeshape as shown in FIG. 28 has been formed on the thermally-oxidized film2A using a photolithography technology, the thermally-oxidized film 2Ais removed by ion etching. While wet etching can be used to remove thethermally-oxidized film 2A, it is preferable to use the ion etching foravoiding the dimensional error due to occurrence of side etching.

Subsequently, the U-like shaped single-crystal silicon substrate 1 onwhich the thermally-oxidized film 2A has been removed is etched byreactive ion etching (RIE) to penetrate the single-crystal siliconsubstrate 1, thereby forming the surrounding space 12.

In the present example, an etching machine provided with ICP(Inductively Coupled Plasma) is used to form the vibrator 11 havingvertical sidewalls according to Bosch process (Bosch company) thatalternately repeats an etching process and film formation process bywhich a sidewall protection film for protecting a sidewall is formed onthe etched portions.

According to the Bosch process, high density plasma has been generatedby ICP. Further, SF₆ gas for etching and C₄F₈ gas for the protection ofsidewall are alternately introduced to perform the etching process at anetching rate of about 10 μm per minute, so that the vibrator 11 havingvertical sidewalls can be formed.

With the above, the formation of the piezoelectric element, shapeformation, and wiring formation, which are the main manufacturing stepsrelated to the formation of the vibration gyro sensor element 10 areterminated. Thus, as shown in FIG. 31, a plurality of (here, 5 by 3)vibration gyro sensor element 10 are formed in the single-crystalsilicon substrate 1.

The number of the vibration gyro sensor elements 10 to be formed in onesingle-crystal silicon substrate 1 is not limited to 5 by 3, as shown inFIG. 31, but is determined by the size of the vibration gyro sensorelements 10 to be designed and the arrangement pitch of the vibrationgyro sensor elements 10.

In the subsequent step, the single-crystal silicon substrate 1 on whichthe plurality of vibration gyro sensor elements 10 have been formed iscut into respective single elements. The method used and dimension individing the plurality of vibration gyro sensor elements 10 formed onthe single-crystal silicon substrate 1 is not particularly limited, andalso the shape obtained after the division is not limited.

In the present example, after dividing marks have been created with adiamond cutter by tracing element dividing lines 20 shown in FIG. 32,the single-crystal silicon substrate 1 is directly folded by hand andrespective vibration gyro sensor elements 10 are taken out. Any methodcan be used as a method of dividing the single-crystal silicon substrate1. For example, it is possible to employ a method of cutting thesingle-crystal silicon substrate 1 by grinding with a grinding stone orcutting it using the surface orientation of the single-crystal siliconsubstrate 1.

Subsequently, as shown in FIG. 33, each of the vibration gyro sensorelements 10 obtained by dividing the single-crystal silicon substrate 1is bonded to an IC substrate 21. The bonding method between thevibration gyro sensor element 10 and IC substrate 21 is not limited, andanaerobic adhesive is used to bond the vibration gyro sensor elements 10to the IC substrate 21 in the present example.

After the bonding, electrical connection between the vibration gyrosensor elements 10 and the IC substrate 21 are allowed to beestablished. On the IC substrate 21, the IC circuit 40 described aboveusing FIG. 2 is mounted. Further, on the IC substrate 21, a substrateterminal 22 a connected to the end portion of the AGC shown in FIG. 2,substrate terminals 22 b and 22 c connected to the synchronous detectioncircuit 45, and a substrate terminal 22 d connected to a not shownreference electrode are formed.

In the present example, the wire connection terminals A, B, C, and D ofthe vibration gyro sensor element 10 are electrically connected to thesubstrate terminals 22 a, 22 b, 22 c, and 22 d within the IC substrate21, respectively using wire bonding. The connection method between themis not particularly limited, and it is possible to employ a method offorming a conducting bump used in a semiconductor as the connectionmethod.

Next, as shown in FIG. 34, a cover member 30 is attached to protect thevibration gyro sensor element 10 and circuit on the IC substrate 21 fromthe outside. While any material can be used as the cover member 30, itis desirable to use a material having shielding effect, such as SUS, inconsideration of influence of the external noise. Further, the covermember 30 needs to have a shape not impeding the vibration of thevibrator 11. Thus, the angular rate sensor 50 has been completed.

When a voltage is applied to the drive electrode 6 a of the vibrator 11included in the vibration gyro sensor element 10 that constitutes theangular rate sensor 50 to allow the vibrator 11 to vibrate at apredetermined resonance frequency, the vibrator 11 vibrates in thevertical direction corresponding to the thickness direction of thevibrator 11 at a vertical resonance frequency, and, at the same time,vibrates in the horizontal direction corresponding to the widthdirection of the vibrator 11 at a horizontal resonance frequency.

In the vibration gyro sensor element 10 shown in FIG. 35, the thicknessof the vibrator 11 is determined by the crystal anisotropic etching asdescribed above, and the side walls of the vibrator 11 are obtained byforming the U-like shaped surrounding space 12 by reactive ion etching.It is ideally desirable that the vibrator 11 be formed into a regularsquare pole having a square cross-section when the vibrator 11 is cutalong a plane perpendicular to the longitudinal direction thereof. FIG.36 shows an ideal cross-section obtained when the vibrator 11 is cutalong the line XX shown in FIG. 35. FIG. 36 is a view showing thecross-section of the vibrator 11 viewed in the direction of an arrow E.When the vibrator 11 has an ideal cross-section, the vibrator has ashape symmetrical with respect to the central axis M.

Although it is ideally desirable that the vibrator 11 have a squarecross-section, the cross-section obtained when the vibrator 11 is cutalong the line XX in FIG. 35 is not symmetrical with respect to thecentral axis M, resulting in a trapezoid-like shape in some cases asshown in FIG. 37.

It is because that when an etching machine provided with ICP(Inductively Coupled Plasma) is used to perform reactive ion etchingincluding Bosch process (Bosch company) that alternately repeats anetching process and sidewall protection film formation process, it isphysically impossible to form the completely vertical side walls.

When a voltage is applied between the reference electrode 4 a and driveelectrode 6 a of the vibrator 11 having an ideal cross-section as shownin FIG. 36 to allow the vibrator 11 to vibrate self-excitedly, thevibrator 11 vibrates in the thickness direction of the vibrator 11 asshown in FIG. 38, that is, vibrates in vertical direction as denoted byan arrow V1 perpendicular to the surface on which the piezoelectric body5 a has been formed.

On the other hand, when a voltage is applied between the referenceelectrode 4 a and drive electrode 6 a of the vibrator 11 whose sidewallshave been formed by reactive ion etching as shown in FIG. 37 to allowthe vibrator 11 to vibrate self-excitedly, it is estimated that thevibrator 11 will vibrate in the direction denoted by an arrow V2 in FIG.39 inclined to the detection electrode 6 b side.

When the vibration direction of the vibrator 11 is inclined as describedin FIG. 39, there arises a difference between detection signals detectedfrom the detection electrodes 6 b and 6 c even in a state where anyangular rate is not applied to the vibration gyro sensor element 10,which undermines the credibility of the value actually detected when theangular rate is applied to the vibration gyro sensor element 10. To bespecific, a larger detection signal is obtained on the side to which thevibration direction is inclined. That is, in FIG. 39, the detectionsignal detected in the detection electrode 6 b becomes larger than thatdetected in the detection electrode 6 c.

Therefore, when the vibration gyro sensor element 10 has been formedaccording to the above-mentioned manufacturing method, it is necessarythat the inclination of the vibration direction of the vibrator 11,which is difficult to avoid, be adjusted to close to the vibrationdirection obtained when the vibrator 11 has an ideal cross-section.

It is very difficult to visually determine the cross-section of thevibrator 11 for adjusting the shape of the vibrator 11 to close to thesquare-shape. Therefore, a voltage is applied between the referenceelectrode 4 a and drive electrode 6 a to allow the vibrator 11 tovibrate self-excitedly at a vertical resonance frequency, the detectionsignals of the detection electrodes 6 b and 6 c obtained at this timeare compared to each other, and a laser light is irradiated to a desiredportion of the vibrator 11 for grinding based on the detection result tochange the shape of the vibrator 11, thereby adjusting the vibrationdirection.

For example, an Ar gas laser machine can be used as the laser machinethat emits a laser light. The present invention is not limited to a typeof the laser machine, and any laser machine can be used as far as it canemit a laser light.

Next, a process of irradiating a laser light for grinding to vibrator 11included in the vibration gyro sensor element 10 shown in FIG. 35 toadjust the vibration direction will be described with reference to aflowchart of FIG. 40.

In step S1, a drive signal is input to the vibration gyro sensor element10 to drive the vibrator 11. More specifically, a voltage is appliedbetween the drive electrode 6 a and reference electrode 4 a through thewire connection terminals A and D to allow the vibrator 11 to vibrateself-excitedly at a vertical resonance frequency.

In step S2, detection signals obtained from the detection electrodes 6 band 6 c when the vibrator 11 vibrates self-excitedly are measured. Forsimplicity of explanation, the detection signal obtained from thedetection electrode 6 b formed on the left side of the vibrator 11 isassumed to be a detection signal L, and the detection signal obtainedfrom the detection electrode 6 c formed on the right side of thevibrator 11 is assumed to be a detection signal R, in FIG. 35.

In step S3, the detection signal L obtained from the detection electrode6 b and the detection signal R obtained from the detection electrode 6 care compared to each other. When the detection signal L is larger thanthe detection signal R (detection signal L>detection signal R), the flowadvances to step S4. Otherwise, the flow advances to step S5.

In step S4, a laser light is irradiated to a predetermined area of thevibrator 11 based on the comparison result of step S3 that the detectionsignal L is larger than the detection signal R to perform grindingoperation.

FIG. 41 is a view when the vibration gyro sensor element 10 is rotatedabout the line XX in FIG. 35 by 180°, that is, a view showing the backsurface of the vibration gyro sensor element 10 when the surface onwhich the various electrode films have been formed is assumed to be thefront surface thereof.

It is basically preferable that the grinding operation using laser lightirradiation to the vibrator 11 be applied to the back surface of thevibration gyro sensor element 10 shown in FIG. 41 to prevent influenceon the electrode films formed on the front surface. When the detectionsignal L is larger than the detection signal R, the vibration directionof the vibrator 11 is inclined to the detection electrode 6 b side fromthe axis perpendicular to the surface on which the piezoelectric body 5a has been formed, as shown in FIG. 39. That is, it is estimated thatthe vibrator 11 has a cross-section asymmetrical with respect to thecentral axis M of the vibrator 11 shown in FIG. 41.

In order to properly adjusting the vibration direction, a laser light isirradiated to a processing area T1 on the right side with respect to thecentral axis M shown in FIG. 41 to perform grinding operation.

It is also possible to adjust the vibration direction by irradiating alaser beam onto the front surface of the vibration gyro sensor element10 on which various electrode films have been formed to grind thevibrator 11, as shown in FIG. 42. Also when a laser light is irradiatedonto the front surface, a processing area of the vibrator 11 is selectedbased on the comparison result of the detection signals L and R, as inthe case of the laser light irradiation onto the back surface. In stepS4, a processing area T3 of FIG. 42 on the left side where the detectionelectrode 6 b has been formed is set as the area to be subjected togrinding operation using laser light irradiation. At this time, laserlight is irradiated such that influence on the various electrode filmsformed on the vibrator 11 is reduced to a minimum level.

After the grinding operation of the vibrator 11 using the laser lightirradiation in step S4, the flow returns to step S2 and the aboveprocess is repeated.

In step S5, the detection signal L obtained from the detection electrode6 b and the detection signal R obtained from the detection electrode 6 care compared to each other. When the detection signal R is larger thanthe detection signal L (detection signal R>detection signal L), the flowadvances to step S6. Otherwise, there is no difference between thedetection signals L and R (detection signal R=detection signal L), sothat the flow is ended.

In step S6, a laser light is irradiated to a predetermined area of thevibrator 11 based on the comparison result that the detection signal Ris larger than the detection signal L to perform grinding operation.

When the detection signal R is larger than the detection signal L, thevibration direction of the vibrator 11 is inclined to the detectionelectrode 6 c side from the axis perpendicular to the surface on whichthe piezoelectric body 5 a has been formed, which is the oppositedirection in step S4. That is, it is estimated that the vibrator 11 hasa cross-section asymmetrical with respect to the central axis M of thevibrator 11 shown in FIG. 41.

In order to properly adjusting the vibration direction, a laser light isirradiated to a processing area T2 on the left side with respect to thecentral axis M shown in FIG. 41 to perform grinding operation.

It is also possible to adjust the vibration direction by irradiating alaser beam onto the front surface of the vibration gyro sensor element10 on which various electrode films have been formed to grind thevibrator 11, as shown in FIG. 42. Also when a laser light is irradiatedonto the front surface, a processing area of the vibrator 11 is selectedbased on the comparison result of the detection signals L and R, as inthe case of the laser light irradiation onto the back surface. In stepS6, a processing area T4 of FIG. 42 on the left side where the detectionelectrode 6 c has been formed is set as the area to be subjected togrinding operation using laser light irradiation. At this time, laserlight is irradiated such that influence on the various electrode filmsformed on the vibrator 11 is reduced to a minimum level.

After the grinding operation of the vibrator 11 using the laser lightirradiation in step S6, the flow returns to step S2 and the aboveprocess is repeated.

In steps S4 and S6 of the flowchart shown in FIG. 40, the areas that alaser beam is irradiated are set on the processing areas T1, T2, T3, andT4 of the vibrator 11. Looking more closely, the laser beam irradiationpoint in the above areas is set in the vicinity of an end portion K forfixing through which the vibrator 11 is fixed to the vibration gyrosensor element 10, or in the vicinity of the sidewall surface 11 b or 11c of the vibrator 11, as shown in FIG. 43.

It is assumed, for example, that the detection signal L detected in thevibration gyro sensor element 10 shown in FIG. 43 is larger than thedetection signal R, and that a laser light is irradiated onto theprocessing area T1 in step S4 in the flowchart of FIG. 40. Further, atthis time, it is assumed that the laser light is irradiated onto thevicinity of the end portion K for fixing or the vicinity of the sidewallsurface 11 c of the vibrator 11. This is because it is possible toreduce the difference between the detection signals L and R with lessnumber of laser light irradiation operations in the case where the laserlight is irradiated onto the vicinity of the end portion K or thevicinity of the sidewall surface 11 b or 11 c of the vibrator 11 ascompared to the case where the laser light is irradiated onto the areaother than the above, under the condition of the same laser irradiationpower and time. In the following, a difference in the number of laserirradiation operations depending on the laser irradiation point will bedescribed.

FIG. 44 shows ratios of the detection signal L to the detection signal Robtained when a laser light is irradiated at a plurality of times ontopoints PY1, PY2, and PY3 along the sidewall surface 11 c of the vibrator11 starting from the vicinity of the end portion K for fixing toward theleading end of the vibrator 11 within the processing area T1 of thevibrator 11 of the vibration gyro sensor element 10 show in FIG. 43.

It can be seen from FIG. 44 that the number of processing cycles, thatis, the number of the laser light irradiation operations onto the pointPY1, which is closest to the end portion K for fixing is markedly lessthan the number of processing cycles onto the point PY3, which isfarthest from the end portion K for fixing, and the laser lightirradiation operations onto the point PY1 can reduce a differencebetween the detection signals L and R at substantially half the numberof times required in the laser light irradiation operations onto thepoint PY3.

FIG. 45 shows ratios of the detection signal L to the detection signal Robtained when a laser light is irradiated at a plurality of times ontopoints PX1, PX2, and PX3 along the end portion K for fixing of thevibrator 11 starting from the vicinity of the sidewall surface 11 ctoward the center of the vibrator 11 within the processing area T1 ofthe vibrator 11 of the vibration gyro sensor element 10 show in FIG. 43.

It can be seen from FIG. 45 that the number of processing cycles, thatis, the number of the laser light irradiation operations onto the pointPX1, which is closest to the sidewall surface 11 c is markedly less thanthe number of processing cycles onto the point PX3, which is farthestfrom the sidewall surface 11 c, and the laser light irradiationoperations onto the point PX1 can reduce a difference between thedetection signals L and R at substantially half the number of timesrequired in the laser light irradiation operations onto the point PX3.

Therefore, after the processing area that a laser beam is irradiated hasbeen set on the processing area T1, T2, T3 or T4, the laser irradiationpoint is set in the vicinity of the end portion K for fixing or in thevicinity of the sidewall surface of the vibrator 11 within the setprocessing area, thereby effectively reducing a difference between thedetection signals L and R. Further, by setting the laser irradiationpoint in the vicinity of the end portion K and in the vicinity of thesidewall surface of the vibrator 11, a difference between the detectionsignals L and R can be reduced most effectively, thereby furtherreducing the number of processing cycles.

Further, in the case where a laser light is irradiated at a plurality oftimes, the laser irradiation point can be set not only in the same pointwithin the processing region, but also the different points. Forexample, after having been set in the vicinity of the end portion K forfixing or the sidewall surface of the vibrator 11 as coarse adjustmentfor the first time, the laser irradiation point can be gradually awayfrom the vicinity of the end portion K for fixing or the sidewallsurface of the vibrator 11 as fine adjustment.

As described above, when there is a difference between the detectionsignals L and R detected when the vibrator 11 included in the vibrationgyro sensor element 10 is allowed to vibrate self-excitedly at avertical resonance frequency are compared to each other, it is estimatedthat the vibrator 11 has an asymmetrical cross-section and the vibratordoes not vibrate self-excitedly in the thickness direction of thevibrator 11, that is, in the direction perpendicular to the plane onwhich the piezoelectric body 5 a has been formed.

By grinding the target area of the vibrator 11 by means of the laserlight irradiation based on the estimation result, it is possible toadjust the vibration direction to the thickness direction of thevibrator 11, that is, the direction perpendicular to the plane on whichthe piezoelectric body 5 a has been formed.

In the present example, the vibration direction of the vibrator isadjusted by applying the grinding operation by means of the laser lightirradiation to the vibrator of the vibration gyro sensor element 10formed by the afore-mentioned method. The present invention is notlimited to this, but can be widely applied to the vibration gyro sensorelement that includes a cantilever vibrator having a lower electrode,piezoelectric thin film, and an upper electrode formed on thesingle-crystal silicon substrate by a thin film formation process anddetects an angular rate using piezoelectric effect of the piezoelectricthin film.

1. A method of manufacturing a vibration gyro sensor element thatincludes a cantilever vibrator having a lower electrode, a piezoelectricthin film, and an upper electrode, and detects an angular rate usingpiezoelectric effect of the piezoelectric thin film, comprising thesteps of: forming a first protective film pattern including a firstopening portion constituted by the lines parallel to and perpendicularto a {110} surface on a first main surface of a single-crystal siliconsubstrate, the first main surface and a second main surface of thesingle-crystal silicon substrate opposite to the first main surfacehaving orientations {100}, and applying crystal anisotropic etching tothe first opening portion until the thickness of the etched portionbecomes the thickness of the vibrator; sequentially forming the lowerelectrode, piezoelectric thin film, and upper electrode in a stackedmanner on the area to become the vibrator, the area being included inthe second main surface opposite to the first main surface that has beensubjected to the crystal anisotropic etching until the thickness of theetched portion becomes the thickness of the vibrator; forming a secondprotective film pattern including a second opening portion having aspace that makes the vibrator to be a cantilever shape on the secondmain surface where the lower electrode, piezoelectric thin film, upperelectrode have been formed, the second opening portion being constitutedby the lines parallel to and perpendicular to the {110} surface, andforming the vibrator by applying reactive ion etching (RIE) to thesecond opening portion; forming, as the upper electrode, a driveelectrode to which a voltage for allowing the vibrator to vibrate isapplied and first and second detection electrodes extending in thelongitudinal direction of the vibrator in parallel to each other suchthat the drive electrode is interposed between the first and seconddetection electrodes and does not contact with the detection electrodes;and irradiating a laser light to a desired portion of the vibrator toapply grinding operation based on detection signals detected in thefirst and second detection electrodes in the case where there is adifference between the detection signals detected in the first andsecond detection electrodes, the detection signals being obtained when avoltage is applied between the lower electrode and drive electrode toallow the vibrator to vibrate at a vertical resonance frequency, where“{ }” is a symbol for collectively representing equivalent surfaceorientations among which the directions are different from each other.2. The method of manufacturing a vibration gyro sensor element accordingto claim 1, wherein the position on the vibrator to be grinded by thelaser light irradiation is set in the vicinity of an end portion forfixing the vibrator.
 3. The method of manufacturing a vibration gyrosensor element according to claim 1, wherein the position on thevibrator to be grinded by the laser light irradiation is set in thevicinity of a sidewall surface of the vibrator that has been formed bythe reactive ion etching.
 4. The method of manufacturing a vibrationgyro sensor element according to claim 1, wherein the position on thevibrator to be grinded by the laser light irradiation is set in thevicinity of the end portion for fixing the vibrator and sidewall surfaceof the vibrator that has been formed by the reactive ion etching.
 5. Amethod of adjusting vibration direction of the vibrator, the vibratorbeing a cantilever vibrator having a lower electrode, a piezoelectricthin film, and an upper electrode formed on a single-crystal siliconsubstrate by a thin film formation process and included in a vibrationgyro sensor element that detects an angular rate using piezoelectriceffect of the piezoelectric thin film, comprising the steps of: forming,as the upper electrode, a drive electrode to which a voltage forallowing the vibrator to vibrate is applied and first and seconddetection electrodes extending in the longitudinal direction of thevibrator in parallel to each other such that the drive electrode isinterposed between the first and second detection electrodes and doesnot contact with the detection electrodes; and irradiating a laser lightto a desired portion of the vibrator to apply grinding operation basedon detection signals detected in the first and second detectionelectrodes in the case where there is a difference between the detectionsignals detected in the first and second detection electrodes, thedetection signals being obtained when a voltage is applied between thelower electrode and drive electrode to allow the vibrator to vibrate ata vertical resonance frequency.
 6. The method of adjusting vibrationdirection of the vibrator according to claim 5, wherein the position onthe vibrator to be grinded by the laser light irradiation is set in thevicinity of an end portion for fixing the vibrator.
 7. The method ofadjusting vibration direction of the vibrator according to claim 5,wherein the position on the vibrator to be grinded by the laser lightirradiation is set in the vicinity of a sidewall surface of thevibrator.
 8. The method of adjusting vibration direction of the vibratoraccording to claim 5, wherein the position on the vibrator to be grindedby the laser light irradiation is set in the vicinity of the end portionfor fixing the vibrator and sidewall surface of the vibrator.